Color display system



Aug. 29, 1967 J. D. MERRYMAN 3,339,015

' COLOR'DISPLAY SYSTEM Filed April 26, 1965 \IIDEO SIGNAL M [a R7' I 050 BURST PHASE I REACTANCE CRYSTAL AMP CONTROL TUBE v OSCILLATOR /YA r r50 LUMINANCE YNCHRQNOUS AMP. DEMODULATOR MX (Y) 1 (1%)) R 4066;?) y) DA/ R3 DIFFERENTIAL AMP 03 0A FIG]. Hv PHASE H.V.

DIFFERENTIAL 'NVERTER AMR SW5 AMP? I 7 I IELECTRON JERRY MERRYMAN, I :ACCELERATI NG I VENTO 5 I ,VOLTAGE BY J A B c 2' United States Patent 3,339,016 COLOR DISPLAY SYSTEM Jerry D. Merryman, Dallas, Tex., assignor to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed Apr. 26, 1965, Ser. No. 450,691 12 Claims. (Cl. 178-54) ABSTRACT OF THE DISCLOSURE Disclosed is a color display system which utilizes a viewing screen including a first phosphor which when energized by an electron beam emits light of a first hue, the brightness of the emitted light varying as a function of beam electron 'energy, and a second phosphor which when energized by an electron beam emits light of a second, different hue, the brightness of which varies as a second predetermined function of beam electron energy, the second function differing substantially from the first function over a range of beam electron energies. The disclosure is particularly directed to a system for providing a hue signal from the NTSC subcarrier which is proportional to a function such as the electron beam impinging on the phosphors to vary the color of the light emitted by the phosphors whereby an image is produced on the viewing screen.

This invention relates to color display systems and more particularly to such a system employing linear modulation of col-or between two hues.

Among the several objects of the present invention may be noted the provision of a color display system which is capable of producing images which subjectively appear to include a continuous range of hues; the provision of such a display system in which the subjective range of hues is produced by linear modulation or mixing of the llght emitted by two phosphors of different hues; the provision of such a system in which the two phosphors are both excited by a single electron beam of variable energy; the provision of such a system in which the two phosphors are differently responsive to electron beams of different energies; the provision of such a system in which the selection of hue can be accomplished at different levels of image brightness; the provision of such a system which is compatible with black and white television broadcasts; the provision of such a system which is relatively simple and inexpensive; the provision of such a system which is highly stable and is reliable. Other objects and features will be in part apparent and in after.

The invention accordingly comprises the apparatus and methods hereinafter described, the scope of the invenpart pointed out hereintion being indicated in the following claims.

In the accompanying drawings in which one of various possible embodiments of the invention is illustrated:

FIGURE 1 is a schematic block diagram illustrating the operation of a color display system which includes a kinescope tube; and

FIGURE 2 is a graph representing the responses of two "phosphors of the viewing screen of the kinescope tube of FIGURE 1, to electron beams of different energies.

Corresponding reference characters indicate corre- 'sponding parts throughout the drawings.

Referring now to FIGURE 1, the display system illustrated there includes a kinescope tube 11 having a viewing screen indicated generally at 13. Viewing screen 13 includes a glass face plate 15 upon which is deposited a phosphor layer 17 which is constituted by a random mixture of discrete red light emitting phosphor particles 19 and discrete cyan light emitting particles 21. Phosphor layer 17 is in turn coated with an electron permeable aluminum film 23 by means of which an electron beam accelerating voltage can be applied to the screen.

The red light emitting phosphor particles 19 and the cyan light emitting particles 21 are differently responsive to electron beams of differing energies over an appreciable range thereof. The brightness or luminosity response function of each of the phosphor particles 19 and 21 in response to different electron accelerating voltages is represented on the graph of FIGURE 2. The luminosity of the red phosphor particles 19 increases nearly linearly, or with only a gentle curvature, as the electron beam accelerating voltage increases. The response function of the cyan particles 21, however, indicates little response at all for relatively low electron accelerating voltages followed by a relatively sharp knee or threshold beyond which the luminosity rises sharply with increasing voltage. This difference in the response functions of the two types of particles is obtained by treating or coating the cyan particles to provide an energy dissipating barrier layer. The barrier layer establishes a voltage or energy threshold which must be overcome before energization of the phosphor is effected and thus accounts for the sharp knee in the response curve of the cyan particles 21. An appropriate coating material for establishing the barrier layer is silicon dioxide. Coatings of silicon dioxide are applied to the cyan phosphor particles by the cracking of an atmosphere of tetraethoxysilane within which the particles are suspended. The relatively steep rate at which the luminsoity of the cyan particles increases with increasing electron voltages above the threshold is provided by employing an increased concentration of cyan phosphor particles 21 relative to the red phosphor particles 19 or by employing an inherently more sensitive phosphor material. 1

Kinescope 11 also includes a neck portion 27 within which is supported an electron beam gun 29. Gun 29 includes a cathode 31 which emits electrons when heated by a suitable heater (not shown). The number of electrons which are emitted from gun 29 as a beam, i.e., the beam intensity, is controlled or modulated by a grid 33. Electrons emitted from gun 29 are accelerated towards screen 13 by an accelerating voltage applied between the gun and screen as described hereinafter. The electron beam is deflected to scan viewing screen 13' by a conventional deflection yoke 35 which includes both horizontal and vertical deflection coils. Kinescope 11 also includes a deflection compensation electrode 37 constituted by an open grid or mesh which is spaced from screen 13 towards gun 29'.

The circuitry illustrated in block diagram form for controlling kinescope 11 is arranged for operation on television signals broadcast according to conventional NTSC standards. The detected video signal is applied at a terminal 39. Since the steps involved in obtaining the video signal (R.F. amplification, frequency conversion, I.F. amplification and detection) are entirely c0nven tional, they are not illustrated or discussed further herein.

The 3.58 megacycle so-called color burst is selectively amplified in a burst amplifier BA. The amplifier burst signal is compared, in a phase control circuit PC, with a signal generated by a 3.58 megacycle crystal oscillator OSC. A reactance tube RT is interconnected with crystal oscillator OSC to selectively vary the frequency of oscillation over a small range. The phase control circuit PC controls the reactance tube RT so as to phase lock the output signal from oscillator OSC to the color burst frequency in the conventional manner.

The videosignal is also applied to a luminance amplifier YA which amplifies the luminance information (Y) contained in the video signal. Finally, the video signal is applied, together with the output signal from the crystal oscillator OSC, to a synchronous demodulator SD. Using the output signal from the crystal oscillator 080 as a time base, the demodulator SD is operative to detect or demodulate the NTSC chrominance subcarrier at a given phase angle. The detected chrominance information provides a signal which is representative of the color record for a predetermined hue corresponding to that angle. In the example illustrated, demodulator SD produces the conventional red minus luminance (RY) signal.

The R-Y signal is combined, in a mixer MX, with the luminance (Y) signal to obtain a pure red signal (R) which is independent of the other signal components, i.e., the blue and green information, which are included within the Y signal. The R signal is thus a long wavelength record of the original scene being televised, that is, its amplitude is proportional to the brightness of the red light component of the composite image.

As the present invention contemplates that the color of the light emitted by the phosphors be controlled substantially independently of brightness, the illustrated embodiment includes circuitry for deriving a function or signal which is representative of color or hue substantially independently of brightness. In the embodiment illustrated, the function employed as being thus representative of color is the ratio A signal (referred to hereinafter as the hue signal) which is substantialy proportional to is obtained as follows.

The R signal is applied to a resistor R1 and a diode D1 connected in series. Resistor R1 provides current drive to diode D1 and the diode, in known manner, provides a voltage signal which is proportional to the logarithm of R (log R). Similarly, the R-Y signal obtained from modulatorSD is applied to a resistor R2 and a diode D2 connected in series to obtain a voltage signal which is proportionalto the logarithm of RY [log (R'Y)].

The voltage signals obtained from the two diodes D1 and D2 are applied to a differential amplifier DA1 which is operative to produce a voltage signal which is proportional to the difference between the two logarithm signals or, equivalently, to the logarithm of their ratio R Y This current signal is applied to an operational amplifier OA provided with resistive negative feedback by means of a resistor R3. Accordingly, the amplifier is operative to produce a voltage output signal which is proportional to the current input signal, i.e.,

This then is the hue signal employed in the present example.

The hue signal is amplified by a high voltage amplifier HV level and is applied, with suitable D.C. bias, to the screen 13 by means of aluminum film 23. The amplification and bias are such that the electron beam accelerating voltage thus developed between gun 29 and screen 13 traverses the range betweenthe points A and C indicated on the abscissa of the graph of FIGURE 2. As is apparent fro-m FIGURE 2, the light emitted from screen 13 in response to an electron beam so accelerated will vary in color or hue depending upon the particular accelerating voltage applied at any given moment. When the accelerating voltage is at the lower end of its range, substantially red light will be emitted while accelerating voltages at the high end of the range will produce light which is mostly cyan in content. At an intermediate voltage, indicated at B on the abscissa of FIGURE 2, the red and cyan light outputs will be equal and, since cyan, is complementary incolor to red, substantially achromatic or white light will be emitted. Accordingly, it can be seen that the color of the light emitted from screen 13 will vary as a function of the i R-Y signal, which signal is a useful representation of the chrominance information received and is substantially independent of the brightness information.

When no chrominance signal is received, as during NTSC compatible black and white transmission, the electron accelerating voltage will remain fixed substantially at the value indicated at B in FIGURE 2 so that a substantially achromatic image is produced in accordance with the luminance information alone.

While varying the accelerating voltage will control the color of the light emitted from screen 13 as explained above, it is also apparent from FIGURE 2 that such variations in voltage will influence the brightness or luminosity of the light produced by the electron beam. To offset or compensate for such unwanted variations in brightness, the

signal is also fed into differential amplifier DA2 in opposition to the luminance (Y) signal obtained from luminance amplifier YA. Thus, the net signal applied to the grid 33 is that which will produce the desired brightness at screen 13 taking into account the particular electron beam accelerating voltage which is present. Accordingly, the brightness of the light emitted from screen 13 will be the desired function of the received luminance information unaffected by the chrominance information. As noted previously, the color of the emitted light is a function of the chrominance or hue information substantially divorced from brightness information.

The variations in electron accelerating voltage also have another effect upon the operation of kinescope 11 in that the accelerating voltage determines the velocities of the electrons and hence also their susceptibility to deflection by the magnetic fields created by yoke 35. To offset and compensate for these variations in deflection, a voltage which is an inverse function of the total accelerating voltage is applied to the compensating electrode 37 by means of a phase inverter PI. The effect of compensating electrode 37 so operated is illustrated in FIG- URE 1 by the lines 40 and 41 which represent, for a given magnetic deflection, the paths of the electron beam when accelerated by relatively high and low accelerating voltages respectively. At a high total accelerating voltage, the inverse signal applied to electrode 37 reduces the field between the gun 29 and the electrode. The electrons thus move at a lower velocity in this region and are subjected to a greater magnetic deflection as shown by the corresponding portion of the line 40. After passing through the grid-like electrode 37, the electrons following beam path 40 are subjected to a strong field, due to the high accelerating voltage remaining to be traversed, and hence change direction so that they approach the screen more directly. At relatively low total accelerating voltages, however, the electrode 37 increases the voltage between gun 39 and the electrode so that the beam is deflected less and hence traverses the path indicated by the line 41. Upon passing through electrode 37, the electrons following beam path 41 are exposed only to a relatively weak electron field since the screen 13 is at a relatively low potential and hence the electrons are not substantially further deflected. By proper choice of the relative magnitudes of the voltages applied to screen 13 and to electrode 37 in relation to the spacing of electrode 37 from the screen, the beam paths 39 and 41 are caused to converge as illustrated. Thus, the total deflection experienced by the electron beam in reaching the screen is unaffected by the variations in electron accelerating voltage which are employed to control image color.

In summary, it can be seen that an electron beam is scanned over a phosphor screen with consistent deflection characteristics. The intensity of the beam is modulated so that the brightness of the light which it produces is a desired consistent function of the received luminance information regardless of the color of the light. Finally, the color of the light generated by the electron beam is controlled in response to the received chrominance information substantially independently of the brightness information.

While in the example the signal taken as representative of chrominance to the exclusion of brightness was the function other functions can be used which bear various relationships to the received chrominance signal. For example, the ratio R/ Y can be used for the hue signal. Similarly, depending upon the characteristics of the phosphors, a nonlinear function of the chrominance signal can be used. For example, the function log R Y which is used as an intermediate signal in the described apparatus, can itself be applied to the screen 13 to obtain an altered color balance corresponding to the logarithmic character of the function.

Similarly, other forms of beam intensity compensation can be used, an example being the application to grid 33 of a signal which represents the product of the luminance signal and the variable electron accelerating voltage. Other forms of beam deflection compensation can also be used, such as supplemental electrostatic or magnetic deflection.

In view of the above, it will be seen that the several bjects of the invention are achieved and other advantageous results attained.

- As various changes could be made in the above ap paratus and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A color display system responsive to luminance information and chrominance information comprising:

a viewing screen including a first phosphor which when energized by an electron beam emits light of a first hue, the emitted light varying in brightness as a first predetermined function of beam electron energy, and a second phosphor which when energized by an electron beam emits light of a second, different hue, the brightness of the light emitted by said second phosphor varying as a second predetermined function of beam electron energy, said second function differing substantially from said first function over at least a predetermined range of beam electron energies;

electron beam gun means for scanning said screen with a beam of electrons thereby to energize said phosphors;

means for modulating the intensity of said electron beam as a function of said luminance information thereby to vary the brightness of the light emitted by said phosphors; and

means for applying an electron accelerating voltage between said gun and said screen and for modulating said voltage to vary beam electron energies over said range as a function of said chrominance information thereby to vary the color of the light emitted by said phosphors whereby an image is produced on said screen, the variations in brightness and color of which are a function of said luminance information and said chrominance information respectively.

2. A color display system as set forth in claim 1 in which said second hue is substantially complementary in color to said first hue.

3. A color display system as set forth in claim 1 in which said first hue is substantially red and said second hue is substantially cyan.

4. A color display system according to claim 1 in which, due to their relative brightness functions, said first phosphor is brighter, than said second phosphor at relatively low electron beam energy and said second phosphor is brighter than said first phosphor at relatively high electron beam energy.

5. A color display system as set forth in claim 1 including means for compensating for changes in scanning deflection produced by said modulation of the electron beam accelerating voltage in response to said chrominance information.

6. A color display system as set forth in claim 1 including a compensating electrode between said gun and said screen and means for applying a voltage which is an inverse function of said accelerating voltage to said electrode to compensate for changes in scanning deflection produced by said modulation of the electron beam accelerating voltage in response to said chrominance information.

7. A color display system as set forth in claim 1 including means for also modulating the intensity of said beam as an inverse function of said accelerating voltage whereby variations in said accelerating voltage do not substantially affect brightness of the light emitted from said screen.

8. In a color television receiver for receiving color broadcasting signals in which a carrier is modulated by luminance information and chrominance information, a color display system comprising:

a viewing screen including a first phosphor which when energized by an electron beam emits light of relatively long wavelengths, the emitted light varying in brightness as a first predetermined function of beam electron energy, and a second phosphor which when energized by an electron beam emits light of relatively short wavelengths, the brightness of the light emitted by said second phosphor varying as a second predetermined function of beam electron energy, said second function differing substantially from said first function with said first phosphor being brighter than said second phosphor at relatively low electron beam energies and said second phosphor being brighter than said first phosphor at relatively high electron beam energies;

electron beam gun means for scanning said screen with a beam of electrons thereby to energize said phosphors;

means for obtaining a first signal which represents substantially said luminance information;

means for obtaining a second signal which represents substantially a long wavelength color record;

means for providing a third signal which represents substantially the ratio of said first and second signals; i

means for amplifying said third signal and applying the amplified signal as an electron accelerating voltage between said gun and said screen thereby to vary the color of the light emitted by said phosphors; and

means for modulating the intensity of said electron beam as a function of said luminance information thereby to vary the brightness of the light emitted by said phosphors whereby an image is produced on said screen the variations in brightness and color of which are a function of said luminance information and said chrominance information respectively.

9. A color television receiver for use with the NTSC color broadcasting system, said receiver comprising:

a viewing screen including a first phosphor which when energized by an electron beam emits light of a given hue, the emitted light increasing in brightness at a first rate with increasing beam electron energy, and a second phosphor which when energized by an electron beam emits light generally complementary in color to that emitted by said first phosphor, the light emitted by said second phosphor increasing in brightness at a second rate which is greater than said first rate with increasing beam electron energy over at least a portion of the range thereof, said phosphors when energized together providing substantially light of said given hue at relatively low beam electron energy and substantially said complementary color light at relatively high beam electron energy, there being an intermediate beam electron energy at which substantially achromatic light is produced;

an electron beam gun;

means for detecting the NTSC luminance signal;

means for synchronously demodulating the NTSC chrominance subcarrier at the phase angle corresponding to said given hue to obtain a chrominance signal;

means for deriving a hue signal which is a function of said chrominance signal and said luminance signal;

means for applying an electron accelerating voltage between said gun and said screen and modulating said voltage as a function of said hue signal;

means for modulating the intensity of the beam of electrons emitted from said gun as a function of said luminance signal and also as an inverse function of said accelerating voltage thereby to offset variations in the luminance of said screen induced by varia tions in beam electron energy;

means for scanning said beam across said screen; and means for controlling beam scanning as a function of said accelerating voltage thereby to offset variations in the deflection of said beam caused by variations in beam electron velocity.

10. A color television receiver as set forth in claim 9 in which said first phosphor emits substantially red light and said complementary color is substantially cyan.

11. A color television receiver as set forth in claim 10 wherein said means for synchronously demodulating the NTSC subcarrier detects substantially the R-Y signal and wherein said means for deriving a hue signal combines said R-Y signal and the Y luminance signal and provides a hue signal which is substantially proportional to the function 12. The method of forming color images, in response to luminance information and chrominance information, on a viewing screen including first and second phosphors which emit light of different hues, said phosphors being differently responsive in brightness to electron beams of different beam electron energies over at least a predetermined range, said method comprising:

scanning said screen with a beam of electrons the intensity of which varies as a function of said luminance information thereby to vary the brightness of light emitted by said phosphors; and

applying an electron accelerating voltage to said beam and modulating said voltage to vary electron energies over said range as a function of said chromiance information thereby to vary the color of the light emitted by said phosphors whereby an image is produced on'said screen, the variations in the brightness and color of which are a function of said luminance and chrominance information respectively.

References Cited UNITED STATES PATENTS 3/ 1944 Wilson 1785.4 6/1958 Bedford 178-5.4

8/1965 Pritchard l785.4 X 11/1966 Kagan 1785.4 X 

1. A COLOR DISPLAY SYSTEM RESPONSIVE TO LUMINANCE INFORMATION AND CHROMINANCE INFORMATION COMPRISING: A VIEWING SCREEN INCLUDING A FIRST PHOSPHOR WHICH WHEN ENERGIZED BY AN ELECTRON BEAM EMITS LIGHT OF A FIRST HUE, THE EMITTED LIGHT VARYING IN BRIGHTNESS AS A FIRST PREDETERMINED FUNCTION OF BEAM ELECTRON ENERGY, AND A SECOND PHOSPHOR WHICH WHEN ENERGIZED BY AN ELECTRON BEAM EMITS LIGHT OF A SECOND, DIFFERENT HUE, THE BRIGHTNESS OF THE LIGHT EMITTED BY SAID SECOND PHOSPHOR VARYING AS A SECOND PREDETERMINED FUNCTION OF BEAM ELECTRON ENERGY, SAID SECOND FUNCTION DIFFERING SUBSTANTIALLY FROM SAID FIRST FUNCTION OVER AT LEAST A PREDETERMINED RANGE OF BEAM ELECTRON ENERGIES; ELECTRON BEAM GUN MEANS FOR SCANNING SAID SCREEN WITH A BEAM OF ELECTRONS THEREBY TO ENERGIZE SAID PHOSPHORS; MEANS FOR MODULATING THE INTENSITY OF SAID ELECTRON BEAM AS A FUNCTION OF SAID LUMINANCE INFORMATION THEREBY TO VARY THE BRIGHTNESS OF THE LIGHT EMITTED BY SAID PHOSPHORS; AND MEANS FOR APPLYING AN ELECTRON ACCELERATING VOLTAGE BETWEEN SAID GUN AND SAID SCREEN AND FOR MODULATING SAID VOLTAGE TO VARY BEAM ELECTRON ENERGIES OVER SAID RANGE AS A FUNCTION OF SAID CHROMINANCE INFORMATION THEREBY TO VARY THE COLOR OF THE LIGHT EMITTED BY SAID PHOSPHORS WHEREBY AN IMAGE IS PRODUCED ON SAID SCREEN, THE VARIATIONS IN BRIGHTNESS AND COLOR OF WHICH ARE A FUNCTION OF SAID LUMINANCE INFORMATION AND SAID CHROMINANCE INFORMATION RESPECTIVELY. 